Methods of fabrication of compound light-guide optical elements having embedded coupling-in reflectors

ABSTRACT

A stack has first and second faces and multiple LOEs that each has two parallel major surfaces and a first plurality of parallel internal facets oblique to the major surfaces. A first block has third and fourth faces and a second plurality of parallel internal facets. The first block and the stack are bonded such that the second face joins the third face and the first and second facets are non-parallel, forming a second block. The second block is cut at a plane passing through the first face, forming a first structure having an interfacing surface. A third block has fifth and sixth faces and a plurality of parallel internal reflectors. The third block and the first structure are bonded such that fifth face joins the interfacing surface and the internal reflectors are non-parallel to all the facets, forming a second structure. Compound LOEs are sliced-out from the second structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Pat. ApplicationNo. 63/235,837, filed Aug. 23, 2021, whose disclosure is incorporated byreference in its entirety herein.

TECHNICAL FIELD

The present invention relates to light-guide optical elements (LOEs),and in particular, methods for manufacturing compound LOEs fortwo-dimensional aperture expansion having embedded coupling-inreflectors.

BACKGROUND OF THE INVENTION

Compound LOEs or “two-dimensional expansion waveguides” have beendescribed in various publications by Lumus Ltd (Israel). In generalterms, these compound LOEs employ two regions, each of which is aparallel-faced block of transparent material (i.e., light-transmittingmaterial) for facilitating the propagation of light corresponding to acollimated image by internal reflection at major surfaces, and includesa set of mutually-parallel, internal, partially-reflective surfaces (or“facets”), which redirect the collimated image light while achievingexpansion of the optical aperture. By combining two such elements withdifferent facet orientations, it is possible to achieve two-dimensionalexpansion of the optical aperture within a single compound element,thereby expanding an input image from an image projector and outputtingthe expanded image over a large area towards the eye of an observer.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide methods of fabrication ofcompound LOEs.

According to the teachings of an embodiment of the present invention,there is provided a method of fabricating a compound light-guide opticalelement (LOE). The method comprises: obtaining a stack having a firstpair of faces and a plurality of LOEs, each of the LOEs having a pair ofmajor parallel surfaces and a first plurality of mutually parallelpartially reflective internal surfaces oblique to the pair of majorparallel surfaces; obtaining a first optical block having a second pairof faces and a second plurality of mutually parallel partiallyreflective internal surfaces; bonding together the first optical blockand the stack such that one of the faces of the first pair of faces isjoined to one of the faces of the second pair of faces and such that thefirst plurality of partially reflective internal surfaces isnon-parallel to the second plurality of partially reflective internalsurfaces, thereby forming a second optical block; cutting the secondoptical block along a cutting plane that passes through the other one ofthe faces of the second pair of faces, thereby forming a first opticalstructure having an interfacing surface at the cutting plane; obtaininga third optical block having a third pair of faces and a plurality ofmutually parallel reflective internal surfaces; bonding together thethird optical block and the first optical structure such that one of thefaces of the third pair of faces is joined to the interfacing surfaceand such that the plurality of reflective internal surfaces isnon-parallel to both the first plurality of partially reflectiveinternal surfaces and the second plurality of partially reflectiveinternal surfaces, thereby forming a second optical structure; andslicing out at least one compound LOE from the second optical structureby cutting the second optical structure through at least two cuttingplanes substantially parallel to the major parallel surfaces ofconsecutive LOEs.

Optionally, the method further comprises: for each sliced-out compoundLOE, polishing external surfaces of the sliced-out compound LOE formedby cutting the optical structure along two consecutive of the cuttingplanes.

Optionally, the first optical block has a pair of parallel faces, andthe second plurality of partially reflective internal surfaces areperpendicular to the pair of parallel faces of the first optical block.

Optionally, the first optical block has a pair of parallel faces, andthe second plurality of partially reflective internal surfaces areoblique to the pair of parallel faces of the first optical block.

Optionally, the first optical block has a third plurality of mutuallyparallel partially reflective internal surfaces non-parallel to thefirst and second pluralities of partially reflective internal surfaces.

Optionally, the first optical block has a first region that includes thesecond plurality of partially reflective internal surfaces and a secondregion that includes the third plurality of partially reflectiveinternal surfaces, the first and second regions of the first opticalblock are nonoverlapping regions.

Optionally, the third plurality of partially reflective internalsurfaces are parallel to the major parallel surfaces of the LOEs.

Optionally, each respective one of the third partially reflectiveinternal surfaces is located in a plane that is approximately halfwaybetween the pair of major parallel surfaces of a respective one of theLOEs.

Optionally, the third plurality of partially reflective internalsurfaces is located between the first and second pluralities ofpartially reflective internal surfaces.

Optionally, the second plurality of partially reflective internalsurfaces is located between the first and third pluralities of partiallyreflective internal surfaces.

Optionally, the first optical block is formed by bonding together firstand second constituent optical blocks that each have a pair of facessuch that one of the faces of the pair of faces of the first constituentoptical block is joined to one of the faces of the pair of faces of thesecond constituent optical block, the first constituent optical blockincludes the second plurality of partially reflective internal surfaces,and the second constituent optical block includes a third plurality ofmutually parallel partially reflective internal surfaces non-parallel tothe first plurality of partially reflective internal surfaces andnon-parallel to the second plurality of partially reflective internalsurfaces.

Optionally, the third optical block and the first optical structure arebonded together such that substantially the entirety of the one of thefaces of the third pair of faces is joined to substantially the entiretyof the interfacing surface.

Optionally, the third optical block and the first optical structure arebonded together such that the one of the faces of the third pair offaces is joined to a fractional portion of the interfacing surface.

Optionally, the third optical block has an additional pair of faces, themethod and the further comprises: obtaining an inert block having firstand second pairs of faces; and bonding together the inert block and thethird optical block such that one of the faces of the first pair offaces of the inert block is joined to one of the faces of the additionalpair of faces of the third optical block, thereby forming a compoundblock having first and second faces, the first face of the compoundblock formed from the one of the faces of the third pair of faces andone of the faces of the second pair of faces of the inert block, and thesecond face of the compound block formed from the other one of the facesof the third pair of faces and the one of the faces of the second pairof faces of the inert block.

Optionally, the method further comprises: obtaining a second inert blockhaving a pair of faces; and bonding together the second inert block andthe compound block such that one of the faces of the pair of faces ofthe second inert block is joined to the second face of the compoundblock.

Optionally, bonding together the third optical block and the firstoptical structure includes: bonding together the compound block and thefirst optical structure such that the first face of the compound blockis joined to the interfacing surface.

Optionally, the method further comprises: obtaining an inert blockhaving a pair of faces; and bonding together the inert block and thethird optical block such that one of the faces of the pair of faces ofthe second inert block is joined to the other one of the faces of thethird pair of faces of the optical block.

Optionally, the stack is a bonded stack of the LOEs and a plurality oftransparent spacer plates, the LOEs and the transparent spacer platesalternate along a length of the stack perpendicular to the majorparallel surfaces of the LOEs.

Optionally, the at least two cutting planes are located in consecutivespacer plates having one of the LOEs therebetween.

There is also provided according to an embodiment of the teachings ofthe present invention a method of fabricating a compound light-guideoptical element (LOE). The method comprises: obtaining a first opticalblock that comprises: at least a first pair of faces, a first regionformed from a stack of LOEs, each of the LOEs having a pair of majorparallel surfaces and a set plurality of mutually parallel partiallyreflective internal surfaces located between the parallel surfaces andinclined obliquely to the parallel surfaces such that the first regioncomprises a first plurality of partially reflective internal surfaces,and a second region having a second plurality of mutually parallelpartially reflective internal surfaces non-parallel to the firstplurality of partially reflective internal surfaces; cutting the firstoptical block along a cutting plane that passes through one of the facesof the first pair of faces, thereby forming a first optical structurehaving an interfacing surface at the cutting plane; obtaining a secondoptical block having a second pair of faces and a plurality of mutuallyparallel reflective internal surfaces; bonding together the firstoptical structure and the second optical block such that one of thefaces of the second pair of faces is joined to the interfacing surfaceand such that the plurality of reflective internal surfaces isnon-parallel to both the first plurality of partially reflectiveinternal surfaces and the second plurality of partially reflectiveinternal surfaces, thereby forming a second optical structure; andslicing out at least one compound LOE from the second optical structureby cutting the second optical structure through at least two cuttingplanes substantially parallel to the major parallel surfaces ofconsecutive LOEs.

Optionally, the stack is a bonded stack of the LOEs and a plurality oftransparent spacer plates, the LOEs and the transparent spacer platesalternate along a length of the stack perpendicular to the majorparallel surfaces of the LOEs.

Optionally, the at least two cutting planes are located in consecutivespacer plates having one of the LOEs therebetween.

Optionally, the first optical block further includes an additional pairof faces, one of major parallel surfaces of the LOE at a top end of thestack forms part of one of the faces of the additional pair of faces,and one of major parallel surfaces of the LOE at a bottom end of thestack forms part of the other one of the faces of the additional pair offaces.

Optionally, the second optical sub-block includes a first sub-blockregion and a second sub-block region, the second plurality of partiallyreflective internal surfaces are located in the first sub-block region,a third plurality of mutually parallel partially reflective internalsurfaces are located in the second sub-block region, and the thirdplurality of partially reflective internal surfaces are non-parallel tothe first plurality of partially reflective internal surfaces andnon-parallel to the second plurality of partially reflective internalsurfaces.

Optionally, the third plurality of partially reflective internalsurfaces is located between the first and second pluralities ofpartially reflective internal surfaces.

Optionally, the second plurality of partially reflective internalsurfaces is located between the first and third pluralities of partiallyreflective internal surfaces.

There is also provided according to an embodiment of the teachings ofthe present invention a method of fabricating a compound light-guideoptical element (LOE). The method comprises: obtaining a first opticalblock having a first pair of faces and a first plurality of mutuallyparallel partially reflective internal surfaces; obtaining a secondoptical block formed as a stack of LOEs and having a second pair offaces, each of the LOEs having a pair of major parallel surfaces and asecond plurality of mutually parallel partially reflective internalsurfaces oblique to the pair of major parallel surfaces; obtaining athird optical block having a third pair of faces and a third pluralityof mutually parallel partially reflective internal surfaces; bondingtogether the first and third optical blocks and bonding together thesecond and third optical blocks to form a fourth optical block, thebonding is such that: i) one of the faces of the first pair of faces isjoined to one of the faces of the third pair of faces, ii) one of thefaces of the second pair of faces is joined to the other one of thefaces of the third pair of faces, iii) the third plurality of partiallyreflective internal surfaces is substantially parallel to the majorparallel surfaces of the LOEs, and iv) the first, second, and thirdpluralities of partially reflective internal surfaces are mutuallynon-parallel; cutting the fourth optical block along a cutting planethat passes through the other one of the faces of the first pair offaces, thereby forming a first optical structure having an interfacingsurface at the cutting plane; obtaining a fifth optical block having afourth pair of faces and a plurality of mutually parallel reflectiveinternal surfaces; bonding together the first optical structure and thefifth optical block to form a second optical structure, the bondingtogether the first optical structure and the fifth optical block is suchthat one of the faces of the fourth pair of faces is joined to theinterfacing surface and such that the plurality of reflective internalsurfaces is non-parallel to the first, second, and third pluralities ofpartially reflective internal surfaces; and slicing out at least onecompound LOE from the second optical structure by cutting the secondoptical structure through at least two cutting planes substantiallyparallel to the major parallel surfaces of consecutive LOEs.

Optionally, the stack is a bonded stack of the LOEs and a plurality oftransparent spacer plates, the LOEs and the transparent spacer platesalternate along a length of the stack perpendicular to the majorparallel surfaces of the LOEs.

Optionally, the at least two cutting planes are located in consecutivespacer plates having one of the LOEs therebetween.

There is also provided according to an embodiment of the teachings ofthe present invention a method of fabricating a compound light-guideoptical element (LOE). The method comprises: obtaining a first opticalblock having a first pair of faces and a first plurality of mutuallyparallel partially reflective internal surfaces; obtaining a secondoptical block formed as a stack of LOEs and having a second pair offaces, each of the LOEs having a pair of major parallel surfaces and asecond plurality of mutually parallel partially reflective internalsurfaces oblique to the pair of major parallel surfaces; obtaining athird optical block having a third pair of faces and a third pluralityof mutually parallel partially reflective internal surfaces; bondingtogether the first and third optical blocks and bonding together thefirst and second optical blocks to form a fourth optical block, thebonding is such that: i) one of the faces of the third pair of faces isjoined to one of the faces of the first pair of faces, ii) one of thefaces of the second pair of faces is joined to the other one of thefaces of the first pair of faces, iii) the third plurality of partiallyreflective internal surfaces is substantially parallel to the majorparallel surfaces of the LOEs, and iv) the first, second, and thirdpluralities of partially reflective internal surfaces are mutuallynon-parallel; cutting the fourth optical block along a cutting planethat passes through the other one of the faces of the third pair offaces, thereby forming a first optical structure having an interfacingsurface at the cutting plane; obtaining a fifth optical block having afourth pair of faces and a plurality of mutually parallel reflectiveinternal surfaces; bonding together the first optical structure and thefifth optical block to form a second optical structure, the bondingtogether the first optical structure and the fifth optical block is suchthat one of the faces of the fourth pair of faces is joined to theinterfacing surface and such that the plurality of reflective internalsurfaces is non-parallel to the first, second, and third pluralities ofpartially reflective internal surfaces, thereby forming a second opticalstructure; and slicing out at least one compound LOE from the secondoptical structure by cutting the second optical structure through atleast two cutting planes substantially parallel to the major parallelsurfaces of consecutive LOEs.

Optionally, the stack is a bonded stack of the LOEs and a plurality oftransparent spacer plates, the LOEs and the transparent spacer platesalternate along a length of the stack perpendicular to the majorparallel surfaces of the LOEs.

Optionally, the at least two cutting planes are located in consecutivespacer plates having one of the LOEs therebetween.

Unless otherwise defined herein, all technical and/or scientific termsused herein have the same meaning as commonly understood by one ofordinary skill in the art to which the invention pertains. Althoughmethods and materials similar or equivalent to those described hereinmay be used in the practice or testing of embodiments of the invention,exemplary methods and/or materials are described below. In case ofconflict, the patent specification, including definitions, will control.In addition, the materials, methods, and examples are illustrative onlyand are not intended to be necessarily limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the present invention are herein described, by wayof example only, with reference to the accompanying drawings. Withspecific reference to the drawings in detail, it is stressed that theparticulars shown are by way of example and for purposes of illustrativediscussion of embodiments of the invention. In this regard, thedescription taken with the drawings makes apparent to those skilled inthe art how embodiments of the invention may be practiced.

Attention is now directed to the drawings, where like reference numeralsor characters indicate corresponding or like components. In thedrawings:

FIGS. 1A - 1C are schematic side, front, and plan views, respectively,of a compound LOE having a first LOE region with a first set ofpartially reflective internal surfaces and a second LOE region with asecond set of partially reflective internal surfaces non-parallel to thefirst set of partially reflective internal surfaces;

FIGS. 2A and 2B are schematic side and front views, respectively, of acompound LOE similar to the compound LOE of FIGS. 1A - 1C, but includinga third region with one or more third partially reflective internalsurfaces;

FIG. 3A is a schematic side view of an optical block formed as a bondedstack of LOEs that can be used to form second LOE regions of compoundLOEs, according to embodiments of the present invention;

FIG. 3B is a schematic side view of one of the LOEs of the stack of FIG.3A;

FIG. 3C is a schematic side view of a bonded stack of coated plates thatcan be cut at predetermined intervals to produce the LOEs of FIG. 3A;

FIG. 3D is a schematic side view of LOEs arranged in a formation priorto bonding to form the stack of FIG. 3A;

FIGS. 4A and 4B are schematic front and isometric views, respectively,of an optical block having a plurality of partially reflective surfacesthat can be used to form first LOE regions of compound LOEs, accordingto embodiments of the present invention;

FIG. 4C is a schematic front view of a bonded stack of coated platesthat can be cut at predetermined intervals to produce the optical blockof FIGS. 4A and 4B;

FIGS. 5A and 5B are schematic front and isometric views, respectively,of an optical block having a plurality of partially reflective surfacesthat can be used to form third LOE regions of compound LOEs, accordingto embodiments of the present invention;

FIG. 5C is a schematic side view of a bonded stack of coated plates thatcan be cut at predetermined intervals to produce the optical block ofFIGS. 5A and 5B;

FIGS. 6A - 6C are schematic isometric, front, and side views,respectively, of the optical blocks of FIGS. 3A, 4A, 4B, 5A, and 5B inalignment prior to being bonded together, according to embodiments ofthe present invention;

FIGS. 7A - 7C are schematic isometric, front, and side views,respectively, corresponding to FIGS. 6A - 6C, showing the optical blocksbonded together to form a new optical block, according to embodiments ofthe present invention;

FIGS. 8A and 8B are schematic isometric and front views, respectively,of a cutting plane along which the optical block of FIGS. 7A - 7C is cutto produce a new optical structure, according to embodiments of thepresent invention;

FIGS. 9A and 9B are schematic isometric and front views, respectively,of the optical structure formed by cutting the optical structure ofFIGS. 8A and 8B along the cutting plane;

FIGS. 10A - 10C are schematic isometric, side, and front views,respectively, of an optical block having a plurality of reflectiveinternal surfaces that can be used to form coupling-in reflectors ofcompound LOEs, according to embodiments of the present invention;

FIG. 10D is a schematic side view of a bonded stack of coated platesthat can be cut at predetermined intervals to produce the optical blockof FIGS. 10A - 10C;

FIGS. 11A and 11B are schematic isometric and front views, respectivelyof the optical structure of FIGS. 9A and 9B and the optical block ofFIGS. 10A - 10C in alignment prior to being bonded together, accordingto embodiments of the present invention;

FIGS. 12A and 12B are schematic isometric and front views, respectively,corresponding to FIGS. 11A and 11B, showing the optical structure andthe optical block bonded together to form a new optical structure,according to embodiments of the present invention;

FIG. 13 is a schematic side view of the optical structure of FIGS. 12Aand 12B showing cutting planes at predetermined intervals along whichthe optical structure can be cut to extract one or more compound LOEs,according to embodiments of the present invention;

FIGS. 14A - 14C are schematic side, front, and plan views, respectively,of a compound LOE sliced-out from the optical structure of FIGS. 12A and12B after cutting the optical structure along two consecutive cuttingplanes of FIG. 13 , according to embodiments of the present invention;

FIG. 15 is a schematic side view of a final compound LOE produced fromthe compound LOE of FIGS. 14A - 14C by polishing two of the majorexternal surfaces of compound LOE of FIGS. 14A - 14C, according toembodiments of the present invention;

FIGS. 16A and 16B are schematic isometric and front views, respectively,of a reduced-sized optical block similar to the optical block of FIGS.10A - 10C, in alignment with first and second inert blocks prior tobeing bonded together with the first inert block, according toembodiments of the present invention;

FIGS. 17A and 17B are schematic isometric and front views, respectively,corresponding to FIGS. 16A and 16B, showing the first inert block andthe optical block bonded together to form a compound block and inalignment with the second inert block prior to the compound block andthe second inert block being bonded together, according to embodimentsof the present invention;

FIGS. 18A and 18B are schematic isometric and front views, respectively,corresponding to FIGS. 17A and 17B, showing the second inert block andthe compound block bonded together to form a second compound block,according to embodiments of the present invention;

FIGS. 19A and 19B are schematic isometric and front views, respectively,similar to FIGS. 12A and 12B, but showing the compound block of FIGS.18A and 18B and the optical structure of FIGS. 9A and 9B bonded togetherto form an optical structure, according to embodiments of the presentinvention

FIG. 20A is a schematic side view similar to FIG. 3D, but showing theLOEs arranged in alternating formation with a plurality of transparentcover plates prior to the LOEs and the transparent cover plates beingbonded together, according to embodiments of the present invention;

FIG. 20B is a schematic side view of the alternating LOEs andtransparent cover plates of FIG. 20A bonded together to form an opticalblock that can be used to form a first LOE region of a compound LOE,according to embodiments of the present invention;

FIG. 21 is a schematic side view of an optical structure similar to theoptical structure of FIG. 13 , but in which the optical structureincludes the optical block of FIG. 20B, according to embodiments of thepresent invention; and

FIG. 22 is a schematic side view of a compound LOE sliced-out from theoptical structure of FIG. 21 after cutting the optical structure alongtwo consecutive cutting planes, according to embodiments of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention provide methods of fabrication ofcompound LOEs.

The principles and operation of the methods according to presentinvention may be better understood with reference to the drawingsaccompanying the description. The accompanying drawings are providedwith an xyz coordinate system that is arbitrarily labeled but which isconsistent between the drawings. This xyz coordinate system is usedherein to better explain the disclosed embodiments by providing a commonreference frame among the drawings.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not necessarily limited in itsapplication to the details of construction and the arrangement of thecomponents and/or methods set forth in the following description and/orillustrated in the drawings and/or the examples. The invention iscapable of other embodiments or of being practiced or carried out invarious ways.

Referring now to the drawings, FIGS. 1A - 1C illustrate various views ofa compound LOE 1. The compound LOE 1 includes a first LOE 10 and asecond LOE 20 that are bonded together at an interface 40. Typically,the two LOEs 10, 20 are manufactured separately and bonded together.Throughout this document, the term “bonded” or “bonding” should beunderstood to mean attached or attaching with an optical cement or glue,or any other suitable adhesive.

The first LOE 10 is formed from a light-transmitting material andincludes a first pair of faces 12 a, 12 b (which may or may not beparallel faces), a second pair of faces (major external surfaces) 14 a,14 b that is a pair of parallel faces, a third pair of faces (majorexternal surfaces) 16 a, 16 b (that may or may not be parallel faces),and a plurality of mutually parallel partially reflective internalsurfaces (also referred to as “facets”) 18 that at least partiallytraverse the LOE 10 between the faces 16 a, 16 b. The LOE 10 isconfigured to guide light (image illumination), corresponding to acollimated image injected into the LOE 10 by an image projector (notshown), such that the light (represented in FIG. 1B by light ray 50) istrapped in one dimension by internal reflection (preferably but notexclusively total internal reflection) at the parallel faces 14 a, 14 bof the LOE 10. The LOE 10 is further configured to gradually couple thepropagating (trapped) light out of the LOE 10 via the facets 18, whichare inclined obliquely to the direction of propagation of the light andeach reflect a proportion of the intensity of the propagating light,thereby expanding the image illumination in one dimension (which in thiscase is approximately along the y-axis). In the drawings, the lightcoupled out of the LOE 10 by the facets 18 is represented by light rays60 (FIGS. 1A and 1B), and the propagation of the collimated image light50 by internal reflection at the faces of the LOE 10 is represented byleft-going and right-going rays 52 (FIG. 1A).

In general, the facets 18 have a first orientation in the compound LOE1. In certain embodiments, the facets 18 are obliquely angled relativeto faces 14 a, 14 b. In other embodiments, the facets 18 are orthogonalto the faces 14 a, 14 b. It is also noted that in certain embodimentsthe facets 18 can be obliquely angled to one or both of the faces 12 a,12 b, whereas in other embodiments the facets 18 can be orthogonal toone or both of the faces 12 a, 12 b. In the nonlimiting exampleembodiment illustrated in FIGS. 1A and 1B, the faces 12 a, 12 b areparallel, and the facets 18 are inclined obliquely to the faces 12 a, 12b.

The reflectivity of the facets 18 can be provided via coatings on theinternal surfaces prior to forming the LOE 10. The reflectance of eachof the facets 18 may be the same, or the reflectivity of the facets 18may be different from one another and may increase along a lightpropagation direction (which in the arbitrarily labeled xyz coordinatesystem in the drawings is along the y-axis).

The light that is coupled out of the LOE 10 is coupled into the secondLOE 20. The LOE 20 is also formed from a light-transmitting material andincludes a first pair of faces 22 a, 22 b (which may or may not beparallel faces), a second pair of faces (major external surfaces) 24 a,24 b that is a pair of parallel faces, a third pair of faces (majorexternal surfaces) 26 a, 26 b (that may or may not be parallel faces),and a plurality of mutually parallel partially reflective internalsurfaces (“facets”) 28 that are inclined obliquely relative to faces 24a, 24 b. The faces 14 a, 24 a are generally coincident (coplanar) so asto form a first singular external face of the compound LOE 1. Likewise,the faces 14 b, 24 b are generally coincident (coplanar) so as to form asecond singular external face of the compound LOE 1. The faces 16 a, 26a are also preferably generally coincident (coplanar) so as to form athird singular external face of the compound LOE 1, and the faces 16 b,26 b are also preferably generally coincident (coplanar) so as to form afourth singular external face of the compound LOE 1. The remaining twoexternal surfaces of the compound LOE 1 are respectively formed from thefaces 12 a and 22 b.

The facets 28 have a second orientation in the compound LOE 1 that isnon-parallel to the first orientation of the facets 18. The reflectivityof the facets 28 can be provided via coatings on the internal surfacesprior to forming the LOE 20. The reflectance of each of the facets 28may be the same, or the reflectivity of the facets 28 may be differentfrom one another and may increase along a light propagation direction(which in the arbitrarily labeled xyz coordinate system in the drawingsis along the x-axis).

The light from LOE 10 is coupled into the LOE 20 through interface 40(which is coincident with the face 12 b and the face 22 a). The LOE 20is configured to guide the light by internal reflection (preferably butnot exclusively total internal reflection) at the faces 24 a, 24 b, andto gradually couple the propagating light out of the LOE 20 via thefacets 28, which each reflect a proportion of the intensity of thepropagating light, toward the eye of an observer, thereby expanding theimage illumination in a second dimension (which in this case is alongthe x-axis). In FIG. 1A, the propagation of image light through the LOE20 by internal reflection at faces 24 a, 24 b is represented by sets ofrays 62, 63. One of the rays 62, 63 represents the image and the otherof the rays 62, 63 represents the image conjugate corresponding to thelight 60 that coupled into the LOE 20 from the LOE 10. The light coupledout of the LOE 20 by the facets 28 is represented in FIG. 1A by lightrays 64.

The image illumination that is to be coupled into the compound LOE 1 forguiding by the LOE 10 and the LOE 20 is generated by an external imageprojector (not shown), which is typically implemented as amicro-projector arrangement formed from a microdisplay device (such asan LCoS chip) that generates image illumination, and collimating opticsfor collimating the image illumination to produce collimated imageillumination. The collimated image illumination is coupled into the LOE10 by a coupling-in optical arrangement, in the form of a highlyreflective internal surface 42 in a coupling-in region of the LOE 10.

In order to fill the LOE 20 with the collimated image illumination(whereby both the image and its conjugate propagate through the LOE byinternal reflection) while maintaining a small input aperture (smallprojector), it is preferable to employ at least one additional partiallyreflective internal surface having a particular orientation relative tothe facets 18, 28 and the faces of the compound LOE. FIGS. 2A and 2Billustrate a compound LOE having such an additional facet 38. The facet38 can be deployed in part of the LOE 10, or as shown in FIGS. 2A and 2Bas part of a separate light-transmitting substrate 30 having three pairsof faces 32 a, 32 b, 34 a, 34 b, 36 a, 36 b (where the pair of faces 34a, 34 b is a pair of parallel faces). The facet 38 is parallel to thefaces 14 a, 14 b, 24 a, 24 b, and thus has an orientation that isnon-parallel to the orientations of the facets 18, 28. When using only asingle facet 38, the facet 38 is preferably located halfway betweenfaces 24 a, 24 b (and equivalently halfway between faces 14 a, 14 b). Ifusing more than one facet 38, the facets 38 are preferably evenly spacedbetween faces 24 a, 24 b. In the embodiment illustrated in FIGS. 2A and2B, the LOE 10 and the substrate 30 are bonded together at faces 12 b,32 a, and the substrate 30 and the LOE 20 are bonded together at faces22 a, 32 b, such that the facet 38 is located between the sets of facets18, 28. It is noted however that other deployments are also possible,for example in which the facets 18 are located between the facet 38 andthe set of facets 28, depending on the design specification of thespecific application for the compound LOE.

In the illustrated embodiment, the light 60 (coupled-out by facets 18)is partially reflected by the facet 38. The reflected and transmittedparts of light 60 are coupled into the LOE 20, and correspond to rays 62and 63, respectively.

Further details of compound LOEs, including compound LOEs that may besimilar to the compound LOEs illustrated in FIGS. 1A - 2B, can be foundin various publications by Lumus Ltd. (Israel), including, for example,U.S. Pat. Application Publication No. 2021/0247608, PCT Publication WO2021/240513, PCT Publication WO 2021/152602, PCT Publication WO2021/001841, and U.S. Pat. No. 10,551,544.

Embodiments of the present invention are directed to methods offabricating compound LOEs. The compound LOEs that are fabricatedaccording to the methods of the present invention may be different instructure from the compound LOEs illustrated in FIGS. 1A - 2B, but havesimilar components, as will become apparent from the ensuingdescription. The fabrication method steps are described in detail belowwith reference to FIGS. 3A - 21 , and generally include steps ofobtaining an optical block 400 (FIGS. 7A - 7C) having sets of therequisite facets 18, 28 (and preferably also a set of facets 38)embedded in regions of the optical block 400 and appropriately orientedrelative to each other such that the facets 18, 28 (and 38) are mutuallynon-parallel, cutting a portion of the optical block 400 at a prescribedcutting plane (FIGS. 8A and 8B) that is at a prescribed angle and passesthrough particular faces of the optical block 400 to form an opticalstructure 400′ having an interfacing surface (FIGS. 9A and 9B) formed atthe cutting plane, obtaining an additional optical block 500 (FIGS.10A - 10D) having a set of reflective internal surfaces 42 embeddedtherein, and bonding the optical block 500 to the optical structure 400′at the interface surface to form an intermediate optical structure 600(FIGS. 12A and 12B) having embedded therein sets of the requisite facets18, 28 (and preferably also a set of facets 38) and a set of thereflective internal surfaces 42 that is non-parallel to the facets 18,28, 38. The intermediate optical structure 600 is then cut along two ormore cutting planes in order to slice-out one or more compound LOEs(FIGS. 13 - 14B), where each compound LOE has facets 18 and facets 28(and preferably also at least one facet 38) and an embedded reflectiveinternal surface 42. Each of the sliced-out compound LOEs can then bepolished to achieve a final compound LOE having a desired thickness(FIG. 15 ). In certain embodiments, one or more blocks 800, 900 of inertmaterial are bonded to the optical block 500 to form a compound block590 (FIGS. 16A - 18B), which is then bonded to the optical structure400′ (FIGS. 19A and 19B) to form the intermediate optical structure 600.As will be discussed, obtaining the optical block 400 can includeproducing the optical block 400 by obtaining various other opticalblocks 100, 200, 300 (FIGS. 3A - 5C) and bonding those optical blocks100, 200, 300 together to form the optical block 400. Each of theoptical blocks 100, 200, 300 has one of the requisite sets of facets 18,28, 38 embedded therein, and can be produced from sets of bonded coatedplates that are cut at appropriate angles and thickness.

It is noted that in the drawings, and in accordance with one set ofnon-limiting embodiments of the present invention, each of the variousblocks 100, 200, 300, 400, 500, 800, 900 is represented as a rectangularcuboid, i.e., a structure having three pairs of parallel faces that aremutually perpendicular (orthogonal). However, such representation of theblocks as rectangular cuboids is for clarity of presentation only, andparallelism and perpendicularity among all of the faces of theindividual blocks is not a strict requirement from an optical standpointor a manufacturing standpoint. In many embodiments, only one pair offaces of a block need be a pair of parallel faces, and the remainingfaces may or may not be parallel. In other embodiments, none of thefaces of a block need be a pair of parallel faces.

The following paragraphs describe the structure and production of theoptical block 200 with reference to FIGS. 3A - 3D. Referring first toFIG. 3A, there is shown the optical block 200, which is formed as astack of LOEs 20 that are bonded together. The optical block 200 has atleast two pairs of faces (major external surfaces), namely a pair ofpreferably parallel faces 212 a, 212 b, and a pair of faces 214 a, 214 bthat is a pair of parallel faces and may be orthogonal (perpendicular)to either or both the faces 212 a, 212 b. The optical block 200 alsoincludes a third pair of faces that may or may not be a pair of parallelfaces, and may also be perpendicular to one or more of the faces 212 a,212 b, 214 a, 214 b. The third pair of faces are not shown in FIG. 3A,but are shown in various other drawings, including FIGS. 6B, 7B, 8B, 9B,11B, 12B, and 19B. As will become apparent, the faces 214 a and 214 bcan respectively form part of upper and lower face of the opticalstructure 600 (FIGS. 11C and 11D) from which a compound LOE can besliced-out.

Each of the LOEs 20 in the stack of FIG. 3A is an LOE as illustrated inFIG. 3B. This LOE 20 is also generally similar to the second LOE 20discussed above with reference to FIGS. 1A -2C. As shown in FIG. 3B, andas discussed above with reference to FIGS. 1A - 2C, each LOE 20 isformed from a light-transmitting material having parallel faces 24 a, 24b and a set (plurality) of internal facets 28 inclined obliquely to thefaces 24 a, 24 b. Such an LOE can be used as a standalone LOE (togetherwith appropriate coupling-in optics) in situations in which apertureexpansion in only one-dimension is desired. This type of LOE is commonlyreferred to as a “one-dimensional” LOE, and the structure and methods ofmanufacturing such one-dimensional LOEs have been described extensivelyin various publications by Lumus Ltd. (Israel), including, for example,U.S. Pat. No. 7,634,214, U.S. Pat. No. 8,873,150, PCT Publication WO2016/103263, and PCT Publication WO 2020/212835.

FIG. 3C shows one example method of fabricating a plurality of LOEs 20,which can be used to produce the optical block 200. In FIG. 3C, aplurality of light-transmitting plates is coated to form coated plates202 which are stacked and bonded together, and then cut along equallyspaced parallel cutting planes 206 (which in the arbitrarily labeled xyzcoordinate system are parallel to the xy plane). Each of the plates 202has a pair of parallel faces (surfaces) 204 a, 204 b which areappropriately coated with coatings that provide the reflectivity of thefacets 28 (such that the facets 28 are partially reflective). Thecutting planes 206 are oblique to the faces 204 a, 204 b and define theoblique angle of the facets 28, and the resulting cuts along the cuttingplanes 206 define the faces 24 a, 24 b of the LOEs 20. The cuttingplanes 206 are spaced at predetermined intervals. Preferably thepredetermined intervals are uniform intervals such that the cuttingplanes 206 are uniformly spaced. The uniform spacing is preferably inthe range of 1-2 millimeters, such that the thickness of each LOE 20(measured between faces 24 a, 24 b) is approximately 1-2 millimeters.

Prior to bonding together the LOEs 20 to form the optical block 200, theLOEs 20 are first aligned and arranged in a formation 210 (FIG. 3D). TheLOEs 20 in the formation 210 are then bonded together to form theoptical block 200 (FIG. 3A) as a bonded stack of LOEs 20, such that thefaces 24 a and 24 b of adjacent (consecutive) LOEs 20 are joinedtogether at bonding regions, and such that the sets of internal facets28 of the LOEs 20 constitute a plurality of facets 28 of the opticalblock 200. As can be seen from FIGS. 3A and 3D, the major surface 24 aof the LOE 20 at the top end of the stack 200 forms the top face 214 aof the stack 200, and the major surface 24 b of the LOE 20 at the bottomend of the stack 200 forms the bottom face 214 b of the stack 200.

The following paragraphs describe the structure and production of theoptical block 100 with reference to FIGS. 4A - 4C. Referring first toFIGS. 4A and 4B, the optical block 100 is formed from alight-transmitting material and has an embedded set of the facets 18.The optical block 100 includes three pairs of faces (major externalsurfaces), namely a pair of faces 112 a, 112 b (which may or may not beparallel faces), a pair of preferably parallel faces 114 a, 114 b, and apair of faces 116 a, 116 b (which may or may not be parallel faces). Incertain embodiments, the pairs of faces of the optical block 100 aremutually orthogonal (perpendicular), which can simplify the fabricationprocess.

The optical block 100 can be formed from a plurality of bonded,transparent coated plates 102 (each plate being formed from alight-transmitting material and coated with a partially reflectivecoating) to form facets 18 that are angled relative to the faces 114 a,114 at a predetermined angle, i.e., the facets 18 may be inclinedobliquely relative to the faces 114 a, 114 b or may be orthogonal to thefaces 114 a, 114 b. The facets 18 may also be inclined obliquely to thefaces 112 a, 112 b at a predetermined angle. Various known methods existfor forming the optical block 100. FIG. 4C illustrates one such method,in which the coated plates 102 are stacked and bonded together (similarto as in FIG. 3C), and then cut along a first pair of preferablyparallel cutting planes 104 and along a second pair of preferablyparallel cutting planes 106 that are preferably perpendicular to theplanes 104, in order to extract the optical block 100. In embodiments inwhich the facets 18 are oblique to one or both of the faces 112 a, 112b, the angle of the cutting planes 104 relative to the faces of thecoated plates 102 determines the angle at which the facets 18 areinclined relative to faces 112 a, 112 b. In addition, the cuts along thecutting planes 104 define the faces 112 a, 112 b of the optical block100, and the cuts along cutting planes 106 define the faces 116 a, 116 bof the optical block 100.

In certain embodiments, such as the embodiment illustrated in FIG. 4C,the cutting planes 104, 106 are perpendicular to the thickness dimensionof the plates 102 such that the resultant facets 18 are perpendicular tothe faces 114 a, 114 b of the optical block 100. In the arbitrarilylabeled xyz coordinate system used in the drawings, when the cuttingplanes 104, 106 are perpendicular to the thickness dimension of theplates 102, the cutting planes 104 are parallel to the yz plane and thecutting planes 106 are parallel to the xz plane. The cutting planes 106are perpendicular to the planes 104.

As noted above, other embodiments are possible in which the facets 18are inclined obliquely to the faces 114 a, 114 b, and as such thecutting planes 106 may be inclined at an appropriate oblique anglerelative to the xz plane to produce the appropriate facet angle relativeto the faces 114 a, 114 b.

The following paragraphs describe the structure and production of theoptical block 300 with reference to FIGS. 5A - 5C. Referring first toFIGS. 5A and 5B, the optical block 300 is formed from alight-transmitting material and has an embedded set of the facets 38.The optical block 300 includes three pairs of faces (major externalsurfaces), namely a pair of faces 312 a, 312 b (which may or may not beparallel faces), a pair of preferably parallel faces 314 a, 314 b, and apair of faces 316 a, 316 b (which may or may not be parallel faces). Incertain non-limiting embodiments, the pairs of faces of the opticalblock 100 are mutually orthogonal (perpendicular).

The optical block 300 can be formed from a plurality of bonded,transparent coated plates 302 (each plate being a formed from alight-transmitting material and coated with a partially reflectivecoating) to form facets 38 that are parallel to faces 314 a, 314 b andoptionally perpendicular to one or both faces 312 a, 312 b. Variousknown methods exist for forming the optical block 300. FIG. 5Cillustrates one such method, in which the coated plates 302 are stackedand bonded (similar to as in FIGS. 3C and 4C), and then cut along a pairof cutting planes 304 in order to extract the optical block 100. Incertain embodiments, such as the embodiment illustrated in FIG. 5C, theplanes 304 are parallel planes (which in the arbitrarily labeled xyzcoordinate system are parallel to the yz plane). However, as alluded toabove, parallelism between the planes 304 is not a strict requirement,and in certain cases it may be advantageous to cut along non-parallelcutting planes, which can improve compactness and overall form factor ofthe final compound LOE product. In certain embodiments, the planes 304are perpendicular to the major external surfaces (faces) of the plates202. However, this perpendicularity is also not an optical requirementfor producing the final compound LOE product, but is rather a matter ofpractical convenience when fabricating the compound LOE. The stacked andbonded plates may also be cut along an additional pair of cutting planes306 that pass through two of the plates, and may be parallel to themajor external surfaces of the plates 202 and perpendicular to planes304. In the arbitrarily labeled xyz coordinate system used in thedrawings, the cutting planes 306 are parallel to the xy plane.

With continued reference to FIGS. 1A - 5C, refer now to FIGS. 6A - 6Cwhich show the three optical blocks 100, 200, 300 prior to being bondedtogether to form the optical block 400 (FIGS. 7A - 7C). Prior tobonding, it is important that the optical blocks 100, 200, 300 areappropriately aligned such that the orientation of the facets 18 isnon-parallel to the orientation of the facets 28, and such that theorientation of the facets 38 is non-parallel to the orientations of thefacets 18, 28. In other words, the blocks 100, 200, 300 are aligned suchthat the facets 18, 28, 38 are mutually non-parallel.

It also preferable that the optical block 300 is aligned with theoptical block 200 such that the facets 38 of optical block 300 are inplanes that are parallel to the planes of faces 214 a, 214 b of theoptical block 200. In embodiments in which each compound LOE is to haveonly a single facet 38, the optical blocks 200 and 300 are preferablyaligned such that each respective facet 38 is located in a plane that isapproximately halfway between the major external surfaces 24 a, 24 b ofa respective one of the LOEs 20 that forms the optical block 200. Inembodiments in which each compound LOE is to have multiple facets 38(say N facets 38), the optical blocks 200 and 300 are preferably alignedsuch for each set of N facets 38, the N facets 38 are evenly spacedbetween the major external surfaces 24 a, 24 b of a respective one ofthe LOEs 20 that forms the optical block 200. It is noted, however, thatthe block 300 can be positioned relative to the block 200 withoutapplying too much scrutiny with respect to the positioning of the facets38 relative to the major external surfaces 24 a, 24 b, and that anymispositioning of the facets 38 relative to the major external surfaces24 a, 24 b in a sliced-out compound LOE can be corrected (typically bypolishing or grinding) at the final stages of fabrication if there areenough spare regions in the sliced-out compound LOE.

With reference to the coordinate system shown in FIGS. 6A - 6C, thealignment of the optical blocks 100, 200, 300 (when each such opticalblock is constructed as a rectangular cuboid) can be understood asfollows: each of the faces 112 a, 212 a, 312 a is in a plane parallel tothe yz plane, each of the faces 112 b, 212 b, 312 b is in a planeparallel to the yz plane, each of the faces 114 a, 214 a, 314 a is in aplane parallel to the xy plane, each of the faces 114 b, 214 b, 314 b isin a plane parallel to the xy plane, each of the faces 116 a, 216 a, 316a is in a plane parallel to the xz plane, and each of the faces 116 b,216 b, 316 b is in a plane parallel to the xz plane. The alignment ofthe optical blocks 100, 200, 300 is also such that each of the facets 38is in a plane that is parallel to the xy plane.

In order to reduce wastage, the optical blocks 100, 200, 300 arepreferably designed to have the same or very close to the samedimensions i.e., length, width, and thickness. In the arbitrarilylabeled xyz coordinate system in the drawings, the length is measuredalong the y-axis, i.e., measured between faces 116 a, 116 b, faces 216a, 216 b, and faces 316 a, 316 b. In the arbitrarily labeled xyzcoordinate system in the drawings, the width is measured along thex-axis, i.e., measured between faces 112 a, 112 b, faces 212 a, 212 b,and faces 312 a, 312 b. In the arbitrarily labeled xyz coordinate systemin the drawings, the thickness is measured along the z-axis, i.e.,measured between faces 114 a, 114 b, faces 214 a, 214 b, and faces 314a, 314 b.

Employing optical blocks 100, 200, 300 having the same thickness (orvery close to the same thickness) is critical to minimizing wastage fromthe final cutting step to slice-out compound LOEs. Therefore, inparticularly preferred embodiments, the alignment of the optical blocks100, 200, 300 is such that the faces 114 a, 214 a, 314 a are coplanar(i.e., lie in a common plane), the faces 114 b, 214 b, 314 b arecoplanar, the faces 112 a, 212 a, 312 a are coplanar, the faces 112 b,212 b, 312 b are coplanar, the faces 116 a, 216 a, 316 a are coplanar,and the faces 116 b, 216 b, 316 b are coplanar.

Once properly aligned, the optical blocks 100, 200, 300 are bondedtogether as illustrated in FIGS. 7A - 7C to form the optical block 400(which is a compound optical block composed of multiple sub-blocks),while maintaining the alignment described with reference to FIGS. 6A -6C. In the illustrated embodiment, the optical block 400 is arectangular cuboid and has three regions, namely one region having theoptical block (stack) 200 which carries the bonded LOEs 20 with facets28, another region having the optical block 300 which carries the facets38, and another region having the optical block 100 which carries thefacets 18. In the illustrated embodiment, the three regions arenon-overlapping, and the three optical blocks 100, 200, 300 have thesame thickness. In such embodiments, the faces 112 a, 212 b form a firstpair of parallel faces 412 a, 412 b of the optical block 400, the face414 a (formed from coplanar faces 114 a, 214 a, 314 a) and the face 414b (formed from coplanar faces 114 b, 214 b, 314 b) form a second pair ofparallel faces of the optical block 400, and the face 416 a (formed fromcoplanar faces 116 a, 216 a, 316 a) and the face 416 b (formed fromcoplanar faces 116 b, 216 b, 316 b) form a third pair of parallel facesof the optical block 400. It is noted that in embodiments in which theblock 400 is not a rectangular cuboid, neither one of the three pairs offaces 412 a, 412 b, 414 a, 414 b, 416 a, 416 b necessarily needs to be apair of parallel faces.

As can be seen from FIGS. 3A, 3D, 7A and 7D, the major surface 24 a ofthe LOE 20 at the top end of the stack 200 forms part of the top face414 a of the optical block 400, and the major surface 24 b of the LOE 20at the bottom end of the stack 200 forms part of the bottom face 414 bof the optical block 400.

In certain embodiments, the optical blocks 100, 200, 300 can be bondedtogether in stages. For example, the optical blocks 200, 300 can bebonded together, and then the optical blocks 100, 300 can be bondedtogether. Alternatively, the optical blocks 100, 300 can be bondedtogether, and then the optical blocks 200, 300 can be bonded together.The optical blocks 200, 300 are bonded together such that the face 312 bis joined to the face 212 a. The optical blocks 100, 300 are bondedtogether such that the face 112 b is joined to the face 312 a. As aresult of the bonding (and proper aligning) of the optical blocks 100,200, 300, the facets 18 are non-parallel to the facets 28.

In certain embodiments, such as the embodiments illustrated in thedrawings, the optical blocks 100, 200, 300 are arranged such that theoptical block 300 is positioned between the optical block 100, 200,resulting in the facets 38 being located between the facets 18, 28.However, other embodiments are possible in which the order of theoptical blocks is different from that shown in the drawings, for examplein which the optical block 100 is positioned between the optical block200, 300, resulting in the facets 18 being located between the facets28, 38. In such embodiments, the face 312 a of the optical block 300forms the face 412 a of the optical block 400.

The embodiments described thus far have pertained to employing threeoptical blocks to form compound optical block 400. However, in certainembodiments the optical block 300 can be omitted or replaced with one ormore optical blocks carrying facets at different orientations from thefacets 38. Therefore, the optical block 400 can generally be consideredas being formed from two optical sub-blocks and having two regions,where the optical block 200 with facets 28 forms a first of thesub-blocks (a first region), and the optical block 100 with facets 18forms a second of the sub-blocks (a second region). In the embodimentsillustrated in the drawings, the second sub-block includes twosub-sub-blocks (two sub-regions), where the facets 18 are located in thefirst sub-sub-block (first sub-region), which in this case is opticalblock 100, and the facets 38 are located in the second sub-sub-block(second sub-region), which in this case is optical block 300.

In embodiments in which optical block 300 is omitted, the optical blocks100, 200 are bonded together to form the optical block 400 such that theface 112 b is joined to the face 212 a. As a result of the bonding (andproper aligning) of the optical blocks 100, 200, the facets 18 arenon-parallel to the facets 28.

With continued reference to FIGS. 1A - 7B, refer now to FIGS. 8A - 9B,which illustrate steps for cutting the optical block 400 (FIGS. 8A and8B) and the result of cutting the optical block 400 (FIGS. 9A and 9B).Generally speaking, and as shown in FIGS. 8A and 8B, the optical block400 is cut along a cutting plane 402 that passes through the face 412 a(which in the illustrated embodiment is face 112 a, but may be face 312a in embodiments in which the positions of the optical blocks 100, 300are exchanged) and at least one of the faces 116 a, 216 a, 316 a. Inembodiments in which the faces 116 a, 216 a, 316 a are coplanar and formthe face 416 a, the cutting plane 402 passes through the face 416 a. Thelocation of the cutting plane 402 is such that the cutting plane 402 atleast passes through a portion of the optical sub-block having thefacets 18 or facets 38. In the illustrated embodiment, the cutting plane402 passes through a portion of the optical sub-block having the facets18, which in the illustrated embodiment is the optical block 100.However, in some practical implementations, the cutting plane 402 maypass through all three regions of the optical block 400 (i.e., passthrough regions which in combination contain facets 18, 38, 28).

In certain embodiments, the cutting plane 402 is oblique to the face 412a (112 a or 312 a), and may also be oblique to one or more of the faces116 a, 316 a, 412 b, 112 b, 312 a, 312 b, 212 a, depending on theconstruction of the optical block 400. The cutting plane 402 ispreferably perpendicular to the face 114 a (and therefore alsoperpendicular to faces 314 a, 214 a in embodiments in which the faces114 a, 314 a, 214 a are parallel). The cutting of the optical block 400along cutting plane 402 results in the formation of an optical structure400′ having an interfacing surface 404 (or “face” 404) at the locationof the cutting plane 402, as illustrated in FIGS. 9A and 9B.

In some of the embodiments in which the optical block 400 comprises thethree optical blocks 100, 200, 300 as illustrated in FIGS. 7A - 7C, thelocation of the cutting plane 402 can be restricted such that thecutting plane 402 only passes through a portion of the optical block 100and does not pass through any of the other optical blocks 200, 300 suchthat the portion to be cut is exclusively part of the optical block 100.However, in other embodiments, the location of the cutting plane 402 maybe such that the cutting plane 402 passes through a portion of theoptical block 300 and may also pass through a portion of the opticalblock 200.

In embodiments in which the faces 116 a, 216 a, 316 a are coplanar andcombine to form the face 416 a, the portion of the optical block 400that is cut-off (i.e., removed) is a triangular prism (typically a righttriangular prism) portion (represented in FIGS. 8A and 8B by 401). Inembodiments in which the optical block 300 is sandwiched between theoptical blocks 100, 200, the portion 401 includes a portion (typicallythe entirety) of the face 116 a and a portion (which may be a minorityportion, for example roughly 10%-20%) of the face 112 a.

In some of the embodiments in which the positions of the optical blocks100, 300 is exchanged such that the optical block 100 is sandwichedbetween the optical blocks 300 and 200, the location of the cuttingplane can be restricted such that the cutting plane 402 only passesthrough a portion of the optical block 300 and does not pass through anyof the other optical blocks 100, 200, such that the portion to be cut isexclusively part of the optical block 300. However, similar to asmentioned above, in certain embodiments the cutting plane 402 may passthrough a portion of the optical block 100 and may also pass through aportion of the optical block 200.

FIGS. 9A and 9B illustrate the optical structure 400′, having theinterfacing surface 404, that is formed as result of cutting the opticalblock 400 along the cutting plane 402 and removing triangular primsportion 401. The optical block 500, having coupling-in reflectors, isbonded to the optical structure 400′ at the interfacing surface 404.

The following paragraphs describe the structure and production of theoptical block 500 with reference to FIGS. 10A - 10D. Referring first toFIGS. 10A - 10C, the optical block 500 is formed from alight-transmitting material and has a set of reflective internalsurfaces 42 (highly reflective mirrors), each of which is used as acoupling-in configuration for the final compound LOE. The optical block500 includes three pairs of faces (major external surfaces), namely apair of preferably parallel faces 512 a, 512 b, a pair of faces 514 a,514 b (which may or may not be parallel faces), and a pair of faces 516a, 516 b (which may or may not be parallel faces). In certainembodiments, the three pairs of faces of the optical block 500 aremutually orthogonal (perpendicular), however, other embodiments may bepreferred in which the pairs of faces are not mutually orthogonal.

The optical block 500 can be formed from a plurality of bonded,transparent coated plates 502 (each plate being formed from alight-transmitting material and coated with a partially reflectivecoating) to form reflective internal surfaces 42 that are inclinedobliquely to either or both of the faces 512 a, 512 b at a predeterminedangle. Various known methods exist for forming the optical block 500.FIG. 10D illustrates one such method, in which the coated plates 502 arestacked and bonded (similar to as in FIGS. 3C, 4C, and 5C), and then cutalong equally spaced parallel cutting planes 504 (which in thearbitrarily labeled xyz coordinate system are parallel to the yz plane)to produce sliced-out optical structures 505. One of the opticalstructures 505 is used to form the optical block 500. Unlike thecoatings used to produce the facets 18, 28, 38, the coatings used toform coated plates 502 are not partially reflective but rather are fully(and preferably highly) reflective, such that the resultant internalsurfaces 42 act as fully reflective mirrors. Dielectric coatings are oneexample of suitable coatings that can be used to form the reflectiveinternal surfaces 42. The cutting planes 504 are obliquely angledrelative to the coated faces the plates 502, where the oblique angle ofthe planes 504 determines the oblique angle at which the internalsurfaces 42 are inclined relative to faces 512 a, 512 b.

In certain embodiments, each of the optical structures 505 can be cutalong two additional parallel planes 506, 508 that are perpendicular toplanes 504 in order to form surfaces 514 a, 514 b such that the opticalblock 500 has a rectangular cross-section. In the arbitrarily labeledxyz coordinate system, the planes 506, 508 are parallel to the xy plane.

With continued reference to FIGS. 8A - 10D, attention is also directedto FIGS. 11A and 11B which show the optical block 500 and the opticalstructure 400′ prior to being bonded together to form optical structure600 (FIGS. 12A and 12B). Prior to bonding, it is important that theoptical block 500 and the optical structure 400′ are appropriatelyaligned such that the orientation of the internal surfaces 42 isnon-parallel to the orientations of the facets 18, 28, 38 (i.e., suchthat the internal surfaces 42 are non-parallel to the facets 18, 28,38), and such that each internal surface 42 is associated with arespective one of the LOEs 20 in the optical block 200 such that theprojection of the internal surface in the thickness dimension of therespective LOE (which in the arbitrarily labeled xyz coordinate systemin the drawings is the yz plane) is bounded by the major surfaces 24 a,24 b of the LOE 20.

In certain embodiments, it may also be preferable that each of the faces514 a, 414 a is in a plane parallel to the xy plane, and that each ofthe faces 514 b, 414 b is in a plane parallel to the xy plane.

In order to avoid wastage at the final cutting step for slicing-out thecompound LOE, the optical block 500 preferably has the same thickness(measured along the z-axis, i.e., between faces 514 a, 514 b) as theconstituent optical blocks 100, 200, 300, and thus the same thickness asthe optical structure 400′. In such embodiments, the alignment of theoptical block 500 with the optical structure 400′ is preferably suchthat the faces 514 a, 414 a are coplanar, as are the faces 514 b, 414 b.In such embodiments, the alignment of the optical block 500 with theoptical structure 400′ is also such that the faces 512 b, 404 arealigned and practically coincident.

Once properly aligned, the optical block 500 and the optical structure400′ are bonded together as illustrated in FIGS. 12A and 12B to formoptical structure 600 (which is an intermediate work product of acompound LOE fabrication process). The bonding of the optical block 500and the optical structure 400′ is such that the face 512 b is joined tothe face (interfacing surface) 404, while maintained the alignmentdescribed above. Preferably, the faces 512 b, 404 are equallydimensioned, or very close to equally dimensioned. In certainembodiments, alignment of the optical block 500 with the opticalstructure 400′ can also include twisting or rotating the face 512 brelative to the interfacing surface 404, such that the internal surfaces42 are tilted at angle relative to the optical structure 400′ inaddition to being inclined relative to either or both of the faces 512a, 512 b. In the drawings, such a tilt angle and inclination anglecorrespond to the internal surfaces 42 being inclined at two anglesrelative to the xy plane.

As illustrated in FIG. 13 , after forming the optical structure 600, theoptical structure 600 is cut (sliced) along two or more preferablyparallel cutting planes 602 at predetermined intervals in order toextract one or more compound LOEs. The cutting planes 602 are preferablyparallel to the major external surfaces 24 a, 24 b of the LOEs 20 thatform the optical block 200. Most preferably, consecutive cutting planes602 are located between the surfaces 24 a, 24 b of consecutive LOEs 20,in particular the bonding regions formed between the surfaces 24 a, 24 bof consecutive LOEs 20. For example, a first 602-1 of the cutting planes602 passes between the bonding region between the second surface 24 b-1of a first one 20-1 of the LOEs 20 and the first surface 24 a-2 of asecond one 20-2 of the LOEs 20 that is adjacent to the first LOE 20-1and bonded to the first LOE 20-1, and a second 602-2 of the cuttingplanes 602 that is adjacent to the first cutting plane 602-1 passesbetween the bonding region between second surface 24 b-2 of the secondLOE 20-2 and the first surface 24 a-3 of a third one 20-3 of the LOEs 20that is adjacent to the second LOE 20-2 and bonded to the second LOE20-2. It is noted herein that the bonding regions (formed between thesurfaces 24 a, 24 b of consecutive LOEs 20) can provide guides forplacement of the cutting planes 602. It is further noted that minordeviations from parallelism of the cutting planes which result in thetwo major surfaces, formed by cutting along consecutive cutting planes602, of a sliced-out compound LOE being approximately parallel but notperfectly parallel can be corrected by polishing the compound LOEs alongthe two major surfaces.

With additional reference to FIGS. 14A - 14C, there is shown onecompound LOE 700 that is sliced-out from the optical structure 600 aftercutting along cutting planes 602. The compound LOE 700 includes a firstpair of faces 712 a, 712 b (that include parts of faces 412 a, 412 b,and which may or may not be parallel faces), a second pair of parallelfaces 714 a, 714 b (major surfaces) formed by cutting the opticalstructure 600 along consecutive cutting planes 602 (and preferablyformed in part by surfaces 24 a, 24 b of one of the LOEs 20), and athird pair of faces 716 a, 716 b (that include parts of faces 416 a, 416b, and which may or may not be parallel faces). Most notably, thecompound LOE 700 has a first plurality of facets 18 (in a first LOEregion 710) having a first orientation and which also may be inclinedobliquely to the faces 714 a, 714 b or orthogonal to the faces 714 a,714 b, a second plurality of facets 28 (in a second LOE region 720)inclined obliquely to the faces 714 a, 714 b and having an orientationnon-parallel to the orientation of the facets 18, and at least one facet38 located in a region 730 between the first and second LOE regions andhaving an orientation parallel to the faces 714 a, 714 b andnon-parallel to the orientations of the facets 18, 28. The compound LOE700 also includes a (highly) reflective internal surface 42 (alsoreferred to as a coupling-in reflector) located in a coupling-in region750 bounded by faces 512 a, 514 a′, 514 b′ 516 a, 516 b, and having anorientation that is non-parallel to the orientations of the facets 18,28, 38 (i.e., reflective internal surface 42 is non-parallel to thefacets 18, 28, 38). Faces 514 a′, 514 b′ are mutually parallel faces andform part of faces 714 a, 714 b. In embodiments in which the face 512 bof the optical block 500 (or face 512 b′ of block 500′ or face 582 ofblock 580/590) is twisted or rotated relative to the interfacing surface404, the reflective surface 42 is tilted about two axes relative to thewaveguide axes (which can be a tilt angle measured relative to thex-axis and the y-axis in the arbitrarily labeled xyz coordinate systemin the drawings).

As should be apparent, unlike the compound LOEs illustrated in FIGS.1A - 2B, the compound LOE 700 does not have a rectangular cross-sectionin the two-dimensional planes (mostly noticeable in the xy plane shownin FIG. 14B), due to the cutting and bonding steps described above withreference to FIGS. 8A - 12B.

After slicing-out the compound LOEs 700, each of the compound LOEs canbe polished on the external surfaces 714 a, 714 b in order to form afinal compound LOE having a desired thickness (measured along the z-axisin the arbitrarily labeled xyz coordinate system in the drawings), andto ensure parallelism between the surfaces 714 a, 714 b (and theoptional facet 38). FIG. 15 shows one view of the resulting polishedcompound LOE, with parallel surfaces 714 a′, 714 b′ corresponding to thesurfaces 714 a, 714 b after being polished.

The compound LOE produced using the fabrication process according to theembodiments disclosed herein provide several advantages over compoundLOEs produced using conventional fabrication methods. First, thelocation of the cutting plane 402 at the specified region of the opticalblock 400 (FIGS. 8A and 8B) accommodates placement of the coupling-inreflector 42 in a region that presents a more aesthetic overall designof the compound LOE 700. In addition, the spatial positioning of thecoupling-in reflector 42, which is determined by the oblique angle ofthe cutting plane 402 and the oblique angle of the cutting planes 504(FIG. 10D), determines the spatial orientation of the image projectorthat produces collimated image light. In the disclosed embodiments, thespatial orientation of the coupling-in reflector 42 can be designed toaccommodate spatial positioning of the image projector below thecompound LOE in association with a portion of the face 714 b′ at or nearthe coupling-in region 750, thereby providing aesthetic placement of theimage projector and reducing the overall formfactor of the opticalsystem formed from the compound LOE and image projector, which can beimplemented as part of a head-mounted display and in certainnon-limiting implementations as part of an eyeglasses formfactor.Furthermore, the reduced wastage of raw materials and the fact that alarge number of compound LOEs can be sliced-out from a single opticalstructure 600 as enabled by the disclosed fabrication processes,facilitates large-scale production of the compound LOEs whilemaintaining lower manufacturing cost compared to conventionalfabrication methods used to produce compound LOEs.

As mentioned, the compound LOE according to the disclosed embodimentscan be attached or otherwise coupled to an image projector that producescollimated image light that can be coupled into the compound LOE by thereflective internal surface 42. In preferred embodiments, thecoupling-in reflector is designed to accommodate spatial positioning ofthe image projector below the compound LOE. For both functional andaesthetic reasons, it is typically desired that the collimated imagerays corresponding to the central field of view chief ray shouldgenerate an approximately perpendicular angle (up to approximately 20°)with relation to the compound LOE both at the input to the compound LOEfrom the image projector (i.e., input to the first LOE region viacoupling-in from the reflective internal surface 42) and at the outputof compound LOE to the eye of the observer (i.e., output from the secondLOE region via facets 28). Accordingly, it is preferable that thereflective internal surface 42 and the facets 28 have similar elevationangle. In other words, the oblique angle of the reflective internalsurface 42 measured relative to the faces 512 a, 512 b is oftenapproximately equal to the oblique angle of the facets 28 measuredrelative to the faces 714 a′, 714 b′ (or equivalently measured relativeto surfaces 24 a, 24 b of the constituent LOE 20 that forms the compoundLOE).

In many cases, only a portion of the reflective internal surface 42provides a useful active area that couples light from the imageprojector into the compound LOE, while the remaining portions of thereflective internal surface 42 either do not couple any light into thecompound LOE, or couple in light at angles which result in unwantedreflections at major surfaces of the compound LOE that give rise toghost images. In addition, the reflective coatings used to form coatedplates 502 (FIG. 10D) for producing reflective internal surface 42typically have a high cost, and therefore reduction of any unused (i.e.,“inactive” ) area of the internal surfaces 42 can reduce manufacturingcosts. Therefore, in order to reduce manufacturing costs and mitigateghost images by preventing or reducing unwanted reflections, it may beadvantageous to limit the size of the reflective internal surfaces 42 tothe active area, and to fill the remaining area with a less expensiveinert material (such as glass, plastic, or even metal).

With additional reference to FIGS. 16A - 18B, the following paragraphsdescribe embodiments in which a reduced-sized reflective internalsurface 42 is produced from a reduced-sized optical block 500′ that isbonded together with one or more blocks 800, 900 of inert material suchas, for example, glass, plastic, or metal. The material used to formblocks 800, 900 (referred to interchangeably herein as “inert blocks”)can be the same or different. For example, both blocks 800, 900 can beformed from glass, or one of the blocks can be formed from glass and theother formed from plastic. The optical block 500′ is similar instructure to the optical block 500, with the noted exception being thatthe length of the optical block 500′ (which in the arbitrarily labeledxyz coordinate system in the drawings is measured along the y-axis) isreduced compared to the length of the optical block 500, therebylimiting the size of the internal surfaces 42 to only the useful activearea. Due to the similarity of the structure of the optical blocks 500′,500, like reference numerals will be used to identify like components,with an apostrophe (“’”) appended to the reference numerals of theoptical block 500′.

The inert block 800 has three pairs of faces (major external surfaces),namely a first pair of preferably parallel faces 812 a, 812 b, a secondpair of faces 814 a, 814 b (which may or may not be parallel faces), anda third pair of faces 816 a, 816 b (which may or may not be parallelfaces). The optical block 500′ is limited in size by the inert block800, and therefore the inert block 800 can be understood to function asa ghost-reducing element, which limits the size of the internal surfaces42 to only the useful active area. In certain embodiments, the block 800is a rectangular cuboid.

The inert block 900 also has three pairs of parallel faces (majorexternal surfaces), namely a first pair of preferably parallel faces 912a, 912 b, a second pair of faces 914 a, 914 b (which may or may not beparallel faces), and a third pair of faces 916 a, 916 b (which may ormay not be parallel faces). In certain embodiments, the block 900 is arectangular cuboid. As will be discussed, the block 900 is optional, butcan be used to advantage to provide structural reinforcement and supportto the optical block 500′.

The bonding is preferably performed in stages, where the optical block500′ and the block 800 are first bonded together to form compound block580. The blocks 500′, 800 are appropriately aligned prior to beingbonded together. With reference to the coordinate system shown in FIGS.16A and 16B, the alignment of the blocks 500′, 800 (when each of theblocks 500′, 800 is constructed as a rectangular cuboid) can beunderstood as follows: the faces 512 a′, 812 a are in a plane parallelto the yz plane and are preferably coplanar, the faces 512 b′, 812 b arein a plane parallel to the yz plane and are preferably coplanar, thefaces 514 a′, 814 a are in a plane parallel to the xy plane and arepreferably coplanar, the faces 514 b′, 814 b are in a plane parallel tothe xy plane and are preferably coplanar, and the faces 516 b′, 816 aare aligned in a plane parallel to the xz plane and are coincident.

The blocks 500′, 800 are bonded together to form compound block 580 suchthat the face 516 b′ is joined to the face 816 a, while maintaining thealignment described with reference to FIGS. 16A and 16B. Block 580 isshown in FIGS. 17A and 17B, and has a first pair of preferably parallelfaces 582 a, 582 b respectively formed from faces 512 a′, 812 a and 512b′, 812 b, a second pair of faces 584 a, 584 b (which may or may not beparallel faces) respectively formed from faces 514 a′, 814 a and 514 b′,814 b, and a third pair of faces 516 a′, 816 b (which may or may not beparallel faces). The internal surfaces 42 are in a first region of theblock 580 and are inclined obliquely to the faces 582 a, 582 b.

In certain embodiments, the blocks 580, 900 can then be bonded togetherto form compound block 590, as illustrated in FIGS. 18A and 18B. Theblocks 580, 900 are appropriately aligned prior to being bondingtogether. With reference to the coordinate system shown in FIGS. 17A and17B, the alignment of the blocks 580, 900 (when each of the blocks 580,900 is constructed as a rectangular cuboid) can be understood asfollows: the faces 516 a′, 916 a are in a plane parallel to the xz planeand are preferably coplanar, the faces 516 b′, 916 b are in a planeparallel to the xz plane and are preferably coplanar, the faces 584 a,914 a are in a plane parallel to the xy plane and are preferablycoplanar, the faces 584 b, 914 b are in a plane parallel to the xy planeand are preferably coplanar, and the faces 582 a, 912 b are aligned in aplane parallel to the yz plane and are coincident.

The blocks 580, 900 are bonded together to form compound block 590 suchthat the face 912 b is joined to the face 582 a, while maintaining thealignment described with reference to FIGS. 17A and 17B. Block 590 isshown in FIGS. 18A and 18B and has a first pair of parallel faces 912 a,582 b, a second pair of faces 594 a, 594 b (which may or may not beparallel faces) respectively formed from faces 914 a, 584 a and 914 b,584 b, and a third pair of faces 596 a, 596 b (which may or may not beparallel faces) respectively formed from faces 916 a, 586 a and 916 b,586 b.

Block 590 can then be aligned and bonded together with the opticalstructure 400′ in place of optical block 500, similar to as describedwith reference to FIGS. 11A - 12B. When using block 590 instead of block500, the bonding of block 590 together with the optical structure 400′is such that the face 582 b is joined to interfacing surface 404, asshown in FIGS. 19A and 19B. As a result, only a fractional portion ofthe interfacing surface 404 is joined to the face 512 b′ (which formspart of face 582 b). This is in contrast to the embodiment illustratedin FIGS. 12A and 12B, in which the entirety of the face 512 b is joinedto the entirety of the interfacing surface 404. The optical structureformed as a result of bonding together block 590 and optical structure400′ can then be sliced at predetermined intervals demarcated byparallel cutting planes in order to extract one or more compound LOEs,similar to as described with reference to FIG. 13 .

In certain embodiments, the inert block 900 can be bonded without theinert block 800 in order to provide structural reinforcement and supportto the optical block 500. For example, in one embodiment, the inertblock 900 and the optical block 500 are bonded together to form anintermediate block such that the face 912 b is joined to the face 512 aof the optical block 500. In such an embodiment, the inert block 900 andthe optical block 500 are appropriately aligned prior to being bondingtogether.

In another similar embodiment, the inert block 900 and the optical block500′ are bonded together without the presence block 800. In such anembodiment, the bonding is such that that the face 912 b is joined tothe face 512 a′ of the optical block 500′. In such an embodiment, theinert block 900 and the optical block 500′ are appropriately alignedprior to being bonding together. Optionally, the size of the inert block900 can be reduced to match the size of the optical block 500′.

In certain embodiments, it may be advantageous to provide a transparentcover plate on either or both of the polished surfaces 714 a′, 714 b′ ofthe sliced-out compound LOE, such as the compound LOE illustrated inFIG. 15 . In certain embodiments, such transparent cover plates can beprovided directly to the surfaces 714 a′, 714 b′ (i.e., after thesliced-out compound LOE is polished).

In other embodiments, the transparent cover plates can be provided asspacer plates between the LOEs 20 during production of the optical block200, as shown in FIGS. 20A and 20B. Looking first at FIG. 20A, there isillustrated an aligned arrangement 220 of LOEs 20 and transparent coverplates 220, in which the LOEs 20 and the cover plates 230 alternatealong a length of the arrangement 220 perpendicular to the parallelfaces 24 a, 24 b of the LOEs 20 (here the length is along the z-axis).Each cover plate 230 has a pair of parallel external faces 231 a, 231 b.The cover plates 230 and the LOEs 20 are bonded together to form abonded stack 200′ (also referred to as optical block 200′), as shown inFIG. 20B. The bonding is such that the faces 231 b, 24 a of adjacentcover plates 230 and LOEs 20 are joined, and such that the faces 231 a,24 b of adjacent cover plates 230 and LOEs 20 are joined.

The stack 200′ is generally similar in structure to the stack 200 ofFIG. 3A (i.e., the stack 200′ has three pairs of parallel faces and isformed from a plurality of bonded LOEs) and the like reference numeralswill be used to denote like elements. One notable difference betweenstacks 200 and 200′ is that the stack 200′ is a bonded stack of LOEs 20and cover plates 230 in which the LOEs 20 and the cover plates 230alternate along a length of the stack 200′ that is perpendicular to thefaces 214 a, 214 b (and parallel to faces 212 a, 212 b). Thesetransparent cover plates 230 are also referred to as transparent spacerplates, as they provide spacing between consecutive LOEs.

In embodiments in which optical block 200′ is provided, having LOEs 20provided with spacer plates 230 therebetween, the thickness of thecoated plates 302 used in forming optical block 300 should be adjustedto account for the overall thickness of the optical block 200′ and toensure that alignment of the optical blocks 200′, 300 results in eachfacet 38 being located in a plane that is halfway between the majorsurfaces 24 a, 24 b of the associated LOE 20 such that the opticalblocks 200′, 300 are bonded together at the proper alignment. Inaddition, when performing the cutting step to slice-out compound LOEswhen employing optical block 200′ instead of optical block 200, theconsecutive cutting planes should pass through consecutive spacer plates230 having one of the LOEs 20 therebetween, as illustrated in FIG. 21 ,and preferably pass approximately through the center of the spacerplates 230.

An example of a sliced-out compound LOE 700 having two transparent coverplates 232, 234 is illustrated in FIG. 22 . The cover plates 232, 234are formed from two of the cover plates 230 in the stack 200′ that aresliced along two of the cutting planes 602. The cover plates 232, 234are bonded to the LOE 20 such that the face 231 b of cover plate 232 isjoined to the face 24 a of LOE 20, and the face 231 a of cover plate 234is joined to the face 24 b of LOE 20. The face 233 a of the cover plate232 (which is opposite face from face 231 b of cover plate 232), and theface 233 b of the cover plate 234 (which is opposite from face 231 a ofcover plate 234) respectively form part of the major external surfaces714 a, 714 b of the compound LOE 700. The surfaces 714 a, 714 b of thecompound LOE of FIG. 22 can then polished, similar to as described abovewith reference to FIG. 15 to achieve a final compound LOE having adesired thickness and to ensure parallelism between the faces 714 a, 714b.

Although the embodiments described herein have pertained to bonding theoptical block 500 (or 500′) to the optical structure 400′ such that thecoupling-in reflector 42 accommodates spatial positioning of the imageprojector below the final compound LOE product, other embodiments arepossible which accommodate different spatial positioning of the imageprojector. For example, the optical block 500 can be inverted (forexample by exchanging the positions of the faces 514 a, 514 b) such thatthe internal surfaces 42 are inclined upward, rather than downward asshown in FIGS. 10A, 10B, 11A, and 12A. Such a configuration allowsdeployment of the image projector above the final compound LOE product.

Although not illustrated in the drawings, additional optical components,such as prisms, can be optically coupled or bonded with the opticalblock 500 (or 500′), with or without inert blocks 800 and/or 900, priorto slicing-out the compound LOE in order to provide additionalcoupling-in geometries of the final compound LOE product. Alternatively,in addition, one or more additional optical components, such as a prism,can be optically coupled or bonded with the coupling-in reflector 42 atthe coupling-in region 750.

The present disclosure has described various cutting steps in whichoptical materials are cut along cutting planes in order to producevarious optical blocks and sub-components of optical blocks. It is notedthat in certain embodiments, some or all of the surfaces that resultfrom these cutting steps can be polished prior to bonding steps. Forexample, the joined faces of the optical blocks 100, 200, 300 can bepolished prior to bonding together the optical blocks 100, 200, 300. Inaddition, the major surfaces of the LOEs used to form the optical block200 can be polished prior to forming the bonded stack of LOEs (opticalblock 200). Furthermore, the interfacing surface 404 and the joiningface of the optical block 500 can be polished prior to bonding togetherthe optical blocks 400, 500.

The alignment of the various blocks and structures described herein canbe performed using any suitable optical alignment apparatus / device(s)/ tool(s) that perform suitable optical alignment techniques / methods.Such suitable optical alignment apparatus / device(s) / tool(s) caninclude, for example, one or more computerized control device, one ormore computerized processing device, one or more optical subsystemhaving, for example, one or more light source, one or more lightdetector/sensor, one or more optics (e.g., one or more lens, foldingoptics, etc.), autocollimators, and the like. Details of non-limitingexamples of suitable optical alignment apparatus / device(s) / tool(s) /method(s) that can be used for aligning the various blocks andstructures described herein can be found in various publications byLumus Ltd. (Israel), including, for example, International PatentApplication No. PCT/IL2021/051377 and International Patent ApplicationNo. PCT/ IL2021/051378, which are unpublished as of the filing date ofthis application and do not constitute prior art.

The cutting or slicing of the optical blocks and the optical structuresdescribed herein can be performed by any suitable cutting apparatus /device / tool, as should be understood by those of ordinary skill in theart. The polishing of the faces and surfaces of the optical blocks andoptical structures (including the compound LOEs) described herein can beperformed by any suitable polishing apparatus / device / tool, as shouldbe understood by those of ordinary skill in the art.

Although the embodiments described thus far have pertained to bondingtogether two or three optical blocks respectively carrying two or threeset of facets at prescribed orientations to accommodate deflection oflight in prescribed directions, other embodiments are contemplatedherein in which one or more additional optical blocks carrying one ormore additional sets of facets or an optical retarder (such as one ormore waveplates) at prescribed orientations are bonded to theaforementioned optical blocks. The scope of the present invention shouldnot be limited to any particular number of the aforementioned opticalblocks.

The descriptions of the various embodiments of the present disclosurehave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

As used herein, the singular form, “a”, “an” and “the” include pluralreferences unless the context clearly dictates otherwise.

The word “exemplary” is used herein to mean “serving as an example,instance or illustration”. Any embodiment described as “exemplary” isnot necessarily to be construed as preferred or advantageous over otherembodiments and/or to exclude the incorporation of features from otherembodiments.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

To the extent that the appended claims have been drafted withoutmultiple dependencies, this has been done only to accommodate formalrequirements in jurisdictions which do not allow such multipledependencies. It should be noted that all possible combinations offeatures which would be implied by rendering the claims multiplydependent are explicitly envisaged and should be considered part of theinvention.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

What is claimed is:
 1. A method of fabricating a compound light-guideoptical element (LOE), comprising: obtaining a stack (200) having afirst pair of faces (212 a, 212 b) and a plurality of LOEs (20), each ofthe LOEs (20) having a pair of major parallel surfaces (24 a, 24 b) anda first plurality of mutually parallel partially reflective internalsurfaces (28) oblique to the pair of major parallel surfaces (24 a, 24b); obtaining a first optical block (100, 300) having a second pair offaces (112 a, 112 b, 312 a, 312 b) and a second plurality of mutuallyparallel partially reflective internal surfaces (18, 3 8); bondingtogether the first optical block (100, 300) and the stack (200) suchthat one of the faces (212 a) of the first pair of faces is joined toone of the faces (112 b, 312 b) of the second pair of faces and suchthat the first plurality of partially reflective internal surfaces (28)is non-parallel to the second plurality of partially reflective internalsurfaces (18, 38), thereby forming a second optical block (400); cuttingthe second optical block (400) along a cutting plane (402) that passesthrough the other one of the faces (112 a, 312 a) of the second pair offaces, thereby forming a first optical structure (400′) having aninterfacing surface (404) at the cutting plane (402); obtaining a thirdoptical block (500) having a third pair of faces (512 a, 512 b, 512 a′,512 b′) and a plurality of mutually parallel reflective internalsurfaces (42); bonding together the third optical block (500) and thefirst optical structure (400′) such that one of the faces (512 b, 512b′) of the third pair of faces is joined to the interfacing surface(404) and such that the plurality of reflective internal surfaces (42)is non-parallel to both the first plurality of partially reflectiveinternal surfaces (28) and the second plurality of partially reflectiveinternal surfaces (18, 38), thereby forming a second optical structure(600′); and slicing out at least one compound LOE (700) from the secondoptical structure (600) by cutting the second optical structure (600)through at least two cutting planes (602) substantially parallel to themajor parallel surfaces (24 a, 24 b) of consecutive LOEs (20).
 2. Themethod of claim 1, further comprising: for each sliced-out compound LOE,polishing external surfaces (714 a, 714 b) of the sliced-out compoundLOE (700) formed by cutting the optical structure (600) along twoconsecutive of the cutting planes (602).
 3. The method of claim 1,wherein the first optical block (100) has a pair of parallel faces (114a, 114 b), and wherein the second plurality of partially reflectiveinternal surfaces (18) are perpendicular to the pair of parallel faces(114 a, 114 b) of the first optical block (100).
 4. The method of claim1, wherein the first optical block (100) has a pair of parallel faces(114 a, 114 b), and wherein the second plurality of partially reflectiveinternal surfaces (18) are oblique to the pair of parallel faces (114 a,114 b) of the first optical block (100).
 5. The method of claim 1,wherein the first optical block (100, 300) has a third plurality ofmutually parallel partially reflective internal surfaces (38)non-parallel to the first and second pluralities of partially reflectiveinternal surfaces (28, 18).
 6. The method of claim 5, wherein the firstoptical block (100, 300) has a first region (100) that includes thesecond plurality of partially reflective internal surfaces (18) and asecond region (300) that includes the third plurality of partiallyreflective internal surfaces (38), wherein the first and second regions(100, 300) of the first optical block (100, 300) are nonoverlappingregions.
 7. The method of claim 5, wherein the third plurality ofpartially reflective internal surfaces (38) are parallel to the majorparallel surfaces (24 a, 24 b) of the LOEs (20).
 8. The method of claim5, wherein each respective one of the third partially reflectiveinternal surfaces (38) is located in a plane that is approximatelyhalfway between the pair of major parallel surfaces (24 a, 24 b) of arespective one of the LOEs (20).
 9. The method of claim 5, wherein thethird plurality of partially reflective internal surfaces (38) islocated between the first and second pluralities of partially reflectiveinternal surfaces (28, 18).
 10. The method of claim 5, wherein thesecond plurality of partially reflective internal surfaces (18) islocated between the first and third pluralities of partially reflectiveinternal surfaces (28, 38).
 11. The method of claim 1, wherein the firstoptical block (100, 300) is formed by bonding together first and secondconstituent optical blocks (100, 300) that each have a pair of faces(112 a, 112 b, 312 a, 312 b) such that one of the faces (112 b, 312 b)of the pair of faces of the first constituent optical block (100, 300)is joined to one of the faces (312 a, 112 a) of the pair of faces of thesecond constituent optical block (300, 100), wherein the firstconstituent optical block (100, 300) includes the second plurality ofpartially reflective internal surfaces (18, 38), and wherein the secondconstituent optical block (300, 100) includes a third plurality ofmutually parallel partially reflective internal surfaces (38, 18)non-parallel to the first plurality of partially reflective internalsurfaces (28) and non-parallel to the second plurality of partiallyreflective internal surfaces (18, 38).
 12. The method of claim 1,wherein the third optical block (500) and the first optical structure(400′) are bonded together such that substantially the entirety of theone of the faces (512 b) of the third pair of faces is joined tosubstantially the entirety of the interfacing surface (404).
 13. Themethod of claim 1, wherein the third optical block (500) and the firstoptical structure (400′) are bonded together such that the one of thefaces (512 b′) of the third pair of faces is joined to a fractionalportion of the interfacing surface (404).
 14. The method of claim 1,wherein the third optical block (500) has an additional pair of faces(516 a′, 516 b′), the method further comprising: obtaining an inertblock (800) having first and second pairs of faces (816 a, 816 b, 812 a,812 b); bonding together the inert block (800) and the third opticalblock (500) such that one of the faces (816 b) of the first pair offaces of the inert block (800) is joined to one of the faces (516 a′) ofthe additional pair of faces of the third optical block (500), therebyforming a compound block (580) having first and second faces (582 b, 582a), the first face (582 b) of the compound block (580) formed from theone of the faces (512 b′) of the third pair of faces and one of thefaces (812 b) of the second pair of faces of the inert block (800), andthe second face (582 a) of the compound block (580) formed from theother one of the faces (512 a′) of the third pair of faces and the oneof the faces (812 a) of the second pair of faces of the inert block(800).
 15. The method of claim 14, further comprising: obtaining asecond inert block (900) having a pair of faces (912 a, 912 b); andbonding together the second inert block (900) and the compound block(580) such that one of the faces (912 b) of the pair of faces of thesecond inert block (900) is joined to the second face (582 a) of thecompound block (580).
 16. The method of claim 14, wherein bondingtogether the third optical block (500) and the first optical structure(400′) includes: bonding together the compound block (580) and the firstoptical structure (400′) such that the first face (582 b) of thecompound block (580) is joined to the interfacing surface (404).
 17. Themethod of claim 1, further comprising: obtaining an inert block (900)having a pair of faces (912 a, 912 b); and bonding together the inertblock (900) and the third optical block (500, 500′) such that one of thefaces (912 b) of the pair of faces of the second inert block (900) isjoined to the other one of the faces (512 a, 512 a′) of the third pairof faces of the optical block (500, 500′).
 18. A method of fabricating acompound light-guide optical element (LOE): obtaining a first opticalblock (400) comprising: at least a first pair of faces (412 a, 412 b), afirst region (200) formed from a stack (200) of LOEs, each of the LOEs(20) having a pair of major parallel surfaces (24 a, 24 b) and a setplurality of mutually parallel partially reflective internal surfaces(28) located between the parallel surfaces (24 a, 24 b) and inclinedobliquely to the parallel surfaces (24 a, 24 b) such that the firstregion (200) comprises a first plurality of partially reflectiveinternal surfaces (28), and a second region (100, 300) having a secondplurality of mutually parallel partially reflective internal surfaces(18, 38) non-parallel to the first plurality of partially reflectiveinternal surfaces (28); cutting the first optical block (400) along acutting plane (402) that passes through one of the faces (412 a) of thefirst pair of faces, thereby forming a first optical structure (400′)having an interfacing surface (404) at the cutting plane (402);obtaining a second optical block (500) having a second pair of faces(512 a, 512 b, 512 a′, 512 b′) and a plurality of mutually parallelreflective internal surfaces (42); bonding together the first opticalstructure (400′) and the second optical block (500) such that one of thefaces (512 b, 512 b′) of the second pair of faces is joined to theinterfacing surface (404) and such that the plurality of reflectiveinternal surfaces (42) is non-parallel to both the first plurality ofpartially reflective internal surfaces (28) and the second plurality ofpartially reflective internal surfaces (18, 38), thereby forming asecond optical structure (600); and slicing out at least one compoundLOE (700) from the second optical structure (600) by cutting the secondoptical structure (600) through at least two cutting planes (602)substantially parallel to the major parallel surfaces (24 a, 24 b) ofconsecutive LOEs (20).
 19. The method of claim 18, wherein the firstoptical block (400) further includes an additional pair of faces (414 a,414 b), wherein one of major parallel surfaces (24 a) of the LOE (20) ata top end of the stack (200) forms part of one of the faces (414 a) ofthe additional pair of faces, and one of major parallel surfaces (24 b)of the LOE (20) at a bottom end of the stack (200) forms part of theother one of the faces (414 b) of the additional pair of faces.
 20. Themethod of claim 18, wherein the second optical sub-block (100, 300)includes a first sub-block region (100, 300) and a second sub-blockregion (300, 100), wherein the second plurality of partially reflectiveinternal surfaces (18, 38) are located in the first sub-block region(100, 300), wherein a third plurality of mutually parallel partiallyreflective internal surfaces (38, 18) are located in the secondsub-block region (300, 100), and wherein the third plurality ofpartially reflective internal surfaces (38, 18) are non-parallel to thefirst plurality of partially reflective internal surfaces (28) andnon-parallel to the second plurality of partially reflective internalsurfaces (18, 38).
 21. The method of claim 20, wherein the thirdplurality of partially reflective internal surfaces (38) is locatedbetween the first and second pluralities of partially reflectiveinternal surfaces (28, 18).
 22. The method of claim 20, wherein thesecond plurality of partially reflective internal surfaces (18) islocated between the first and third pluralities of partially reflectiveinternal surfaces (28, 38).
 23. A method of fabricating a compoundlight-guide optical element (LOE): obtaining a first optical block (100)having a first pair of faces (112 a, 112 b) and a first plurality ofmutually parallel partially reflective internal surfaces (18); obtaininga second optical block (200) formed as a stack (200) of LOEs (20) andhaving a second pair of faces (212 a, 212 b), each of the LOEs (20)having a pair of major parallel surfaces (24 a, 24 b) and a secondplurality of mutually parallel partially reflective internal surfaces(28) oblique to the pair of major parallel surfaces (24 a, 24 b);obtaining a third optical block (300) having a third pair of faces (312a, 312 b) and a third plurality of mutually parallel partiallyreflective internal surfaces (38); bonding together the first and thirdoptical blocks (100, 300) and bonding together the second and thirdoptical blocks (200, 300) to form a fourth optical block (40 0), whereinthe bonding is such that: i) one of the faces (112 b) of the first pairof faces is joined to one of the faces (312 a) of the third pair offaces, ii) one of the faces (212 a) of the second pair of faces isjoined to the other one of the faces (312 b) of the third pair of faces,iii) the third plurality of partially reflective internal surfaces (38)is substantially parallel to the major parallel surfaces (24 a, 24 b) ofthe LOEs (20), and iv) the first, second, and third pluralities ofpartially reflective internal surfaces (18, 28, 38) are mutuallynon-parallel; cutting the fourth optical block (400) along a cuttingplane (402) that passes through the other one of the faces (112 a) ofthe first pair of faces, thereby forming a first optical structure(400′) having an interfacing surface (400) at the cutting plane (402);obtaining a fifth optical block (500) having a fourth pair of faces (512a, 512 b, 512 a′, 512 b′) and a plurality of mutually parallelreflective internal surfaces (42); bonding together the first opticalstructure (400′) and the fifth optical block (500) to form a secondoptical structure (600), wherein the bonding together the first opticalstructure (400′) and the fifth optical block (500) is such that one ofthe faces (512 b, 512 b′) of the fourth pair of faces is joined to theinterfacing surface (404) and such that the plurality of reflectiveinternal surfaces (42) is non-parallel to the first, second, and thirdpluralities of partially reflective internal surfaces (18, 28, 38); andslicing out at least one compound LOE (700) from the second opticalstructure (600) by cutting the second optical structure (600) through atleast two cutting planes (602) substantially parallel to the majorparallel surfaces (24 a, 24 b) of consecutive LOEs (20).
 24. A method offabricating a compound light-guide optical element (LOE): obtaining afirst optical block (100) having a first pair of faces (112 a, 112 b)and a first plurality of mutually parallel partially reflective internalsurfaces (18); obtaining a second optical block (200) formed as a stack(200) of LOEs (20) and having a second pair of faces (212 a, 212 b),each of the LOEs (20) having a pair of major parallel surfaces (24 a, 24b) and a second plurality of mutually parallel partially reflectiveinternal surfaces (28) oblique to the pair of major parallel surfaces(24 a, 24 b); obtaining a third optical block (300) having a third pairof faces (312 a, 312 b) and a third plurality of mutually parallelpartially reflective internal surfaces (38); bonding together the firstand third optical blocks (100, 300) and bonding together the first andsecond optical blocks (100, 200) to form a fourth optical block (400),wherein the bonding is such that: i) one of the faces (312 b) of thethird pair of faces is joined to one of the faces (112 a) of the firstpair of faces, ii) one of the faces (212 a) of the second pair of facesis joined to the other one of the faces (112 b) of the first pair offaces, iii) the third plurality of partially reflective internalsurfaces (38) is substantially parallel to the major parallel surfaces(24 a, 24 b) of the LOEs (20), and iv) the first, second, and thirdpluralities of partially reflective internal surfaces (18, 28, 38) aremutually non-parallel; cutting the fourth optical block (400) along acutting plane (402) that passes through the other one of the faces (312a) of the third pair of faces, thereby forming a first optical structure(400′) having an interfacing surface (400) at the cutting plane (402);obtaining a fifth optical block (500) having a fourth pair of faces (512a, 512 b, 512 a′, 512 b′) and a plurality of mutually parallelreflective internal surfaces (42); bonding together the first opticalstructure (400′) and the fifth optical block (500) to form a secondoptical structure (600), wherein the bonding together the first opticalstructure (400′) and the fifth optical block (500) is such that one ofthe faces (512 b, 512 b′) of the fourth pair of faces is joined to theinterfacing surface (404) and such that the plurality of reflectiveinternal surfaces (42) is non-parallel to the first, second, and thirdpluralities of partially reflective internal surfaces (18, 28, 38),thereby forming a second optical structure (600); and slicing out atleast one compound LOE (700) from the second optical structure (600) bycutting the second optical structure (600) through at least two cuttingplanes (602) substantially parallel to the major parallel surfaces (24a, 24 b) of consecutive LOEs (20).
 25. The method of claim 1, whereinthe stack (200) is a bonded stack of the LOEs (20) and a plurality oftransparent spacer plates (230), wherein the LOEs (20) and thetransparent spacer plates (230) alternate along a length of the stack(200) perpendicular to the major parallel surfaces (24 a, 24 b) of theLOEs (20).
 26. The method of claim 25, wherein the at least two cuttingplanes (602) are located in consecutive spacer plates (0230) having oneof the LOEs (20) therebetween.